There are many instances where an intraocular lens (IOL) is inserted into eye. For example, the crystalline lens within a person's eye may become clouded due to cataract. The clouded lens may be surgically removed and replaced with an IOL. The IOL may, in addition, be used to provide refractive vision correction.
Pseudophakic monovision is a method of correcting presbyopia by using IOLs to correct the dominant eye for distance vision and the non-dominant eye for near vision in an attempt to achieve spectacle-free binocular vision from far to near. The goal is emmetropia in the dominant eye and myopia (e.g., 1.5 to 2.5 D of defocus) in the non-dominant eye, i.e., high contrast distance and near vision. The use of standard monofocal IOLs in pseudophakic monovision procedures can be problematic for a variety of reasons. For example, standard monofocal IOLs do not preserve natural accommodation. Given that the target refraction is emmetropia in the dominant eye and myopia in the non-dominant eye, a large degree of anisometropia is needed to obtain excellent near visual acuity. The result is, however, a loss of near stereopsis, poor intermediate visual acuity, uncomfortable monocular suppression of visual input.
One example of a conventional pseudophakic monovision procedure, where the IOL for the near vision eye has a power that is 2.0 D greater than the IOL power required to achieve emmetropia in the distance eye, is illustrated in FIGS. 1A and 1B. The IOLs are aspheric IOLs that eliminate (or at least substantially eliminate) the spherical aberration of the eye to provide high levels of contrast and visual acuity. It should also be noted that unless otherwise indicated, when the power difference between the eyes is described herein, both eyes have the same biometry (i.e., the same corneal curvature measured by keratometry and the same axial length), and therefore require the same IOL to be implanted in each eye for emmetropia. Also, the 2.0 D difference mentioned above is the diopter power of the IOL, i.e., is in the IOL plane. The resulting difference in the refractive power of the eye, i.e., in the corneal plane, is slightly different. The corneal plane values are presented in FIGS. 1A and 1B (as well as the similar procedural representations described below). For example, and referring to FIGS. 1A and 1B, 2.0 D greater IOL will result in a myopic defocus of about 1.3 D, depending upon the biometry of the eye. Also, for illustrative purposes only, visual acuity VA of 0.5 (i.e., 20/40 vision) is considered to be the minimum acceptable value. Referring to FIG. 1A, best focus for the distance and near eyes is 0.2 D and 1.5 D, respectively, and the near eye has acceptable visual acuity up to 1.9 D of defocus. Much of the intermediate visual acuity is below 1.0 (i.e., below 20/20 vision), as shown in FIG. 1B. Also, as should be apparent from the FIG. 1B, there could be a loss of stereoacuity if there was more than 2.0 D of defocus in the near eye.